maf can do that, or a vac leak. the check engine light come on?
sounds like the trans got hot and started to act up again. bleed and top off your coolant as well, that could be the temp spike.
these engines typically will get hot in traffic or stop and go driving, and on the open road drop back to a cooler temp.
my regal runs at 1/4 on the temp, and as high as 1/2 way. back and fourth all the time. i have no numbers on my gauge, like your gp.